Oxygen mask comfort is an important issue for many aircrew, life support technicians, and oxygen equipment designers. Extended wear of masks under certain flight conditions continues to be necessary. An oronasal mask used for delivery of gases must be suitable for continuous wear for eight hours, and seal effectively to the face, preventing excessive inboard or outboard leakage of gas. The standard aircrew oxygen mask is equipped with two main structural components which determine the quality of fit for an individual--an external hard-shell and a silicone rubber face piece which forms the seal around the individual's nose and mouth. The hard-shell supports the internal face piece and provides structural support for inhalation and exhalation valves, the supply hose, microphone, and the mask suspension system. The face piece conforms to the hard-shell and incorporates the reflective edge seal which is pressed firmly against the face when positive pressure is delivered to the mask. If the seal is not maintained and mask pressure is lost, the anti-G (acceleration) protection (PBG) and high altitude protection (PBA) provided by positive pressure breathing is also lost, placing aircrew at risk for loss of consciousness.
For positive pressure to be maintained in the lung, a mask must create a near perfect seal around the mouth and nose. Pressures as high as 60 mm Hg are generated by the U.S. Air Force's PEG system, known as the Combined Advance Technology Enhanced Design G Ensemble (COMBAT EDGE). Other PEG and PBA systems use breathing pressures as high as 70 mm Hg. In addition, maintaining the seal as mask weight increases during +Gz is another challenge, particularly during PEG. Mask function during high acceleration forces may be a problem for aircrew who are normally able to achieve a comfortable fit at +1 Gz. The mask must function during exposures of up to +9 Gz, remain in place on the face, maintain a good seal to the skin and not interfere significantly with breathing.
With the advent of PEG and PBA positive pressure, the function and comfort of a mask are inversely related. Nearly any individual can be fitted with a standard off-the-shelf mask size if the absence of a leak is the only criterion for a good fit. For some persons, however, the discomfort due to mask tensioning pressure required to achieve an airtight seal is intolerable. For many individuals, mask discomfort may range somewhere between intolerable and bearable and aircrew performance may suffer.
For these persons the silicon rubber reflective seal fails to maintain a mask seal. Downward slippage on the face causes the seal to be forced outward and away from the face. This condition is partially correctable through additional mask tensioning and hard shell trimming. Increased strap tension, however, usually results in increased discomfort or even pain. The degree of leakage and discomfort of a properly fitted mask is dependent on the individual's facial structure. A proper aircrew oxygen mask fit is often difficult to achieve since each individual's face shape is unique, while only three or four standard mask sizes exist. The existing equipment is not designed to compensate for all variations in facial structure. Sizing systems for oxygen masks are based upon 1950's aircrew anthropometry and are only designed to fit approximately 95% of the target male population. Fitting has become increasingly difficult as females and aircrew of greater ethnic diversity assume combat aircraft roles. Increasing the number of available off-the-shelf sizes is not a cost efficient method of increasing the population coverage of mask fit.
The need therefore exists for a means of customizing standard masks to improve the seal while maintaining a comfortable fit. Applicants' invention is directed towards the solution of this problem by providing a conformal mask insert which supports the mask reflective seal from the inside of the mask cavity, pressing the reflective seal against the user's face at all points. U.S. Pat. No. 5,143,061 describes a supplemental rubber seal which augments the existing mask seal by providing additional sealing surface; however, this supplemental seal does not control the shape of, nor provide additional support to, the existing mask seal. Applicant's invention supports the backside of the existing mask seal and controls the shape of the sealing surface by providing constant pressure across the backside of the seal. Applicant's insert increases the surface contact area of the seal, evenly distributing seal pressure over a broad area of the user's face. A good seal is more easily achieved with the insert, requiring less strap tension. Therefore, comfort is improved over the existing equipment which relies upon increased strap tension to achieve an adequate seal. Applicant's invention provides the solution for those individuals who are unable to achieve a non-leaking comfortable fit with standard mask sizes.
The insert may allow a means of customizing the mask, quickly and reversibly, to benefit a relatively large proportion of the user population. The strong, flexible insert is easily but securely inserted into and removed from the mask cavity without any disassembly of existing mask components. Since the insert is relatively inexpensive and not permanently fixed to the mask, it can be used on an as-needed basis, easily removed for cleaning and maintenance and replaced periodically, if necessary. Additional benefits of the insert may include decreased mask cavity dead space (by approximately 50 ml) and perhaps improved acoustics within the mask cavity. The insert may also alleviate problems with pressure on the nose bridge for certain individuals. The mask with insert is fitted, tested, and used in the same manner as a mask without an insert as prescribed in existing technical publications.
The mask insert concept may benefit any mask design which creates an airtight seal by means of a reflective seal. Modification of the shape of the insert would allow it to be placed into any reflective seal oxygen mask design, thereby improving the comfort and function of masks for commercial and general aviation aircrew, chemical protection respirators used in industry, firefighters respirators, or any face masks which employ a reflective seal to maintain an airtight fit.
These, and other objects, features and advantages of the present invention will become apparent as the detailed description of a preferred embodiment thereof proceeds.